Optimal CO2 is based on the individual aquarium in question.
A low light tanks with a shop light over it, maybe 1-2 bulbs, well, the CO2 demand is not going to be great.
A similar tank with more light that's strongly PO4 limited, will also have less CO2 demand.
A very high light tank and plenty of ferts, and also very intense plant growth, well..........you will need more CO2.
So there's no one single optima for all tanks.
For most densely planted moderate light tanks with reasonable ferts, 30 ppm is a good target to start with. But the chart may not be accurate due to the tap water treatment for SOME tap water suppliers, while it's likely okay for others.
Optimal CO2 is pretty much done by eyeballing it. Looking at the plants, growth and fish/livestock health.
You get close with measurements as best you can, then the rest is a slow progressive increase/decrease and watch closely over the next few days before deciding to add more/less etc. There's no hard no# associated with CO2 really. And it's not something you can easily measure and dial in. You need to work at it.
You need to know the signs of poor CO2, in plants, in algae and with livestock.
Unfortunately, this means experience. Which newbies and folks with issues rarely have